[PATCH RESEND 13/30] KVM: x86: lapic: don't allow to change APIC ID when apic acceleration is enabled

[Maxim Levitsky]

No normal guest has any reason to change physical APIC IDs, and
allowing this introduces bugs into APIC acceleration code.

Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
 arch/x86/kvm/lapic.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index dd4e2888c244b..7ff695cab27b2 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2002,10 +2002,20 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
 
 	switch (reg) {
 	case APIC_ID:		/* Local APIC ID */
-		if (!apic_x2apic_mode(apic))
-			kvm_apic_set_xapic_id(apic, val >> 24);
-		else
+		if (apic_x2apic_mode(apic)) {
 			ret = 1;
+			break;
+		}
+		/*
+		 * Don't allow setting APIC ID with any APIC acceleration
+		 * enabled to avoid unexpected issues
+		 */
+		if (enable_apicv && ((val >> 24) != apic->vcpu->vcpu_id)) {
+			kvm_vm_bugged(apic->vcpu->kvm);
+			break;
+		}
+
+		kvm_apic_set_xapic_id(apic, val >> 24);
 		break;
 
 	case APIC_TASKPRI:
@@ -2572,10 +2582,16 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
 static int kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
 		struct kvm_lapic_state *s, bool set)
 {
-	if (apic_x2apic_mode(vcpu->arch.apic)) {
-		u32 *id = (u32 *)(s->regs + APIC_ID);
-		u32 *ldr = (u32 *)(s->regs + APIC_LDR);
+	u32 *id = (u32 *)(s->regs + APIC_ID);
+	u32 *ldr = (u32 *)(s->regs + APIC_LDR);
 
+	if (!apic_x2apic_mode(vcpu->arch.apic)) {
+		/* Don't allow setting APIC ID with any APIC acceleration
+		 * enabled to avoid unexpected issues
+		 */
+		if (enable_apicv && (*id >> 24) != vcpu->vcpu_id)
+			return -EINVAL;
+	} else {
 		if (vcpu->kvm->arch.x2apic_format) {
 			if (*id != vcpu->vcpu_id)
 				return -EINVAL;
-- 
2.26.3